Fly Agaric

A large conspicuous mushroom, Amanita muscaria is generally common and numerous where it grows, and is often found in groups with basidiocarps in all stages of development. Fly agaric fruiting bodies emerge from the soil looking like a white egg, covered in the white warty material of the universal veil. Dissecting the mushroom at this stage will reveal a characteristic yellowish layer of skin under the veil which assists in identification. As the fungus grows, the red color appears through the broken veil and the warts become less prominent; they do not change in size but are reduced relative to the expanding skin area. The cap changes from globose to hemispherical, and finally to plate-like and flat in mature specimens.[31] Fully grown, the bright red cap is usually around 8–20 cm (3–8 in) in diameter, although larger specimens have been found. The red color may fade after rain and in older mushrooms. After emerging from the ground, the cap is covered with numerous small white to yellow pyramid-shaped warts. These are remnants of the universal veil, a membrane that encloses the entire mushroom when it is still very young. The free gills are white, as is the spore print. The oval spores measure 9–13 by 6.5–9 μm, and are non-amyloid, that is, they do not turn blue with the application of iodine.[32] The stipe is white, 5–20 cm high (2–8 in) by 1–2 cm (0.4–0.8 in) wide, and has the slightly brittle, fibrous texture typical of many large mushrooms. At the base is a bulb that bears universal veil remnants in the form of two to four distinct rings or ruffs. Between the basal universal veil remnants and gills are remnants of the partial veil (which covers the gills during development) in the form of a white ring. It can be quite wide and flaccid with age. There is generally no associated smell other than a mild earthiness.[33][34]

Although very distinctive in appearance, the fly agaric has been mistaken for other yellow to red species in the Americas, including Armillaria cf. mellea and the edible Amanita basii—a Mexican species similar to A. caesarea of Europe. Poison control centers in the U.S. and Canada are aware that amarill is a common name for A. caesarea-like species in Mexico, not just the Spanish for 'yellow'.[22] Amanita caesarea can be distinguished as it has an entirely orange to red cap, lacking the numerous white warty spots of the fly agaric. Furthermore the stem, gills and ring are bright yellow, not white.[35] Finally the volva is a distinct white bag, not broken into scales.[36] In Australia, the introduced fly agaric may be confused with the native vermilion grisette (Amanita xanthocephala), which grows in association with eucalypts. The latter species generally lacks the white warts of A. muscaria and bears no ring.